For the purpose of weight savings in automobiles, it has been considered and carried out, e.g., to replace the material of a component comprised by a steel sheet or the like with a light material, such as an aluminum alloy sheet. In this case, it is necessary to ensure the required stiffness as a prerequisite of the weight savings.
In order to increase the stiffness of a sheet material without increasing the thickness of the sheet, it has been considered to increase the stiffness in a geometric manner by providing a concave-convex pattern in the sheet material.
For example, one component of an automobile is a component formed by a sheet material known as a heat insulator. In Patent Document 1 a material is proposed that has a large number of convex portions formed thereon through embossing in order to ensure sufficient stiffness without increasing thickness. Moreover, in addition to the heat insulator, sheet materials having stiffness increased by forming a concave-convex section through embossing or the like have been proposed for various applications (Patent Documents 2 to 6).